Test of cheap Li-Ion 18650 cells - beware of fakes

I decided to test some Li-Ion cells in 18650 size available on the market (especially on Ebay)
and to find out the truth about their parameters, especially the capacity :).
For testing, I used my battery analyzer.
It turns out that buying the cheapest battery with the highest capacity isn't worth it.
The declared capacity of the battery often does not correspond to reality. The actual capacity can be up to 25x less!
Sometimes it is even technically impossible to fit the declared capacity into the size of a 18650 Li-Ion battery.
We often see Li-Ion cells with the capacity like 5800 mAh, 9900 mAh or even 12 000 mAh. In fact, 18 650 size Li-Ion batteries can't have
higher capacity than 3500mAh. It's just not technically possible. Usually the real 18650 cells tend to have a capacity of about 1800 - 2500 mAh.
There are also 3400 mAh cells, but the higher capacity is at the expense of lower allowed discharge currents.
Therefore, even in the modern cordless drills and other tools
we still see cells with only 2000 mAh capacity. If you see a 18650 Li-Ion cell over 3500 mAh, the capacity is fake.
The maximum capacity may improve with progress, but very slowly.

Also the weight of the battery can tell a lot. Real 18650 Li-Ion cells weigh about 44 grams. If the weight is lower, something is simply missing inside.
Most fakes I came accross weigh only about 24 grams. It is almost 2x less. You can tell it even just by holding it in your hand.
Fake cells are made in low quality and a considerable part of the space inside is empty. Capacity is very low, they don't last long.
Internal resistance is high, they can't supply much current. Additionally, due to poor quality materials, it may have a high self-discharge.
Fake batteries often say they have a built-in protection circuit, although they don't have any. Text on a fake cell often contains typos.
As I test more batteries, I add them to the table below. It appears that the typical capacity of a fake Ebay Li-Ion 18650 cell is only about 400-550 mAh
which makes them almost useless. Fake batteries try to attract the buyers by unreal, sky high capacity, fictive protective circuit and interesting printing.
Real batteries can also be bought for a good price. However, they are mostly hidden behind very simple printing and a low capacity.
The capacity just seems low in a comparison with fake batteries.
The higher is the declared capacity, the lower usually is the real one :).

I measure the capacity at 500mA discharge current down to 3V. Before the test, I charge them at 500mA to 4,2V. The results: